1. Field of the Invention
The present invention relates generally to heat exchangers, and particularly to a double heat exchanger having plural heat exchange cores. The present invention is suitably applied to a double heat exchanger combining a condenser of a refrigeration cycle for a vehicle air conditioner and a radiator for cooling engine coolant.
2. Related Art
Generally, in a double heat exchanger having plural heat exchange cores, a specification of one of the heat exchange cores does not necessarily conform to a specification of the other. Conventionally, a double heat exchanger has a condenser core and a radiator core in which a corrugated condenser fin and a corrugated radiator fin are integrally formed. In such a heat exchanger, when plural condenser tubes and plural radiator tubes are arranged in a vertical direction at the same pitch and a height of each of the radiator tubes is larger than that of each of the condenser tubes in the vertical direction, a height of the condenser fin disposed between adjacent condenser tubes needs to be larger than that of the radiator fin disposed between adjacent radiator tubes in the vertical direction.
However, since the condenser fin is integrally formed with the radiator fin, a longitudinal length of the condenser fin when flattened to a flat plate is necessarily equal to that of the radiator fin. Therefore, a height of the condenser fin can not be simply increased by increasing only the longitudinal length of the condenser fin.
JP-A-11-148795 discloses a double heat exchanger in which a height of a corrugated radiator fin is made larger than that of a corrugated condenser fin by setting a radius of curvature of each wave of the radiator fin smaller than that of each wave of the condenser fin. However, generally, in a multi-flow type heat exchanger having plural tubes, the tubes and plural fins are alternately layered to be tentatively assembled and then integrally brazed in a furnace. Therefore, when a radius of curvature of each wave of the condenser fin is different from that of the radiator fin, an amount of deformation of the condenser fin caused by a force of constraint applied to the condenser fin during an assembling process of the condenser fin and condenser tubes becomes different from that of the radiator fin, even if the condenser fin and the radiator fin are made of the same material and has the same plate thickness. As a result, a contact pressure between the condenser fin and each of the condenser tubes may be largely different from a contact pressure between the radiator fin and each of radiator tubes, thereby causing a fin-tube brazing failure.
Further, when a radius of curvature of each wave of the fin is decreased, a filler is restricted from being formed at a connection portion between the fin and the tube during brazing. Therefore, an area of heat transfer from the tube to the fin is decreased, thereby declining heat exchange performance of the heat exchanger.